1. Field of the Invention
This invention relates to the use of current limiting elements and positive temperature coefficient resistivity elements (PTC elements) in circuit breakers.
2. Description of the Related Art
Circuit breakers are widely used in residential and industrial applications for the interruption of electrical current in power lines upon conditions of severe overcurrent caused by short circuits or ground faults. One of the problems associated with the current interruption process during severe overcurrent conditions is arcing. Arcing, which is highly undesirable for several reasons, occurs between the contacts of circuit breakers used to interrupt the current. Arcing causes deterioration of the contacts and gas pressure to build up within the breaker. Arcing also necessitates circuit breakers with larger separation between the contacts in the opened position to ensure that the arc does not persist with the contacts in the fully opened position.
A circuit breaker normally has a magnetic tripping (xe2x80x9cmag-tripxe2x80x9d) function which is performed by a coil or solenoid. When the current through the circuit breaker reaches a value higher than a predetermined value, for example, about 500% of the ampere rating, the circuit breaker trips instantaneously because of the magnetic force generated by the coil. The predetermined current value is the mag-level of the circuit breaker.
Present circuit breaker designs fail to address the fact that, absent a current limiting device, almost 100% of the interruption energy goes to generate an arc and pressure in the circuit breaker. This arc and pressure can create difficulties in the circuit breaker and end-use equipment. Additionally, an excessive magnetic force generated by a coil in present circuit breaker designs can result in armature damage upon tripping of the circuit breaker.
The apparatus and method of the present invention prevents the generation of excessive magnetic forces in circuit breaker coils and suppresses interruption energy by including a current limiting device which can be incorporated into or separate from the circuit breaker.
An apparatus and method for interrupting the flow of electrical current in a line is disclosed. The invention provides for better limitation of current than can be achieved in the prior art. With effective current limitation the magnetic force generated by the circuit breaker coil will not be excessive, thereby reducing potential damage to the circuit breaker armature, increasing the interruption rating of the circuit breaker and end-use equipment and decreasing the interruption pressure within the circuit breaker.